This type of fan is well known and was first proposed in 1892 by MORTIER for the ventilation of coal mines. The leading feature of the fan is that it has a humped pressure-flow characteristic, the increasing section of which represents between 50 and 75% of the maximum accessible range (or excursion) in terms of flow. The second particular feature is that its zero flow pressure is different from zero. Another characteristic of this fan is the simultaneous supply of high flow and pressure coefficients, compared with a centrifugal fan which, for an equal size, supplies only a high pressure coefficient for low flow coefficient and the axial fan which, conversely and for equal size, only supplies a high flow coefficient at a low pressure coefficient. Consequently, the aeraulic power supplied by the transverse fan is far superior. The weak point of the fan is, traditionally, the efficienty obtained which can be improved by adjusting the stator shapes.
For information, refer to patent DE-A-1 428 071 relative to a cross flow fan with a stable air flow characteristic and which has a low noise feature.
Reference may also be made to patent DE-A-2 545 036 which is an improvement to the fan covered by the previous patent with a complex system of guide walls and porous walls placed on the fluid flow to reduce noise. However, this advantage may be compromised by the clogging of the porous walls after a certain period of use.
There is also a patent FR-A-2 481 378 designed to reduce the noise level and supply an increased air flow for the same rotor speed through a particular rounded shape of the downstream scroll and of the scroll and cross-head leading edge.
However, not that these three documents concern domestic equipment in which the air flow is less than 0.05 m.sup.3 /s with pressure less than 50 Pa.
There is also a device for the ventilation of fluid radiators and rheostats of a driving element using a cross flow fan. However, these relate more particularly to the incorporation of the fan into a structure where little space is available.
In these prior constructions, the flow properties of the cross flow fan are used more particularly and no attempt has ever been made to improve the shapes of the convergent inlet and downstream diffuser to simultaneously obtain high flow and pressure while achieving high yield. A first attempt was made in a theoretical study published by G. HEID, Revue Francaise de Mecanique 1986-2, relating to the application of BIDARD's theory relative to compressor surge, to the study of surge phenomena in cross flow fans. Indeed, all the known designs of cross flow fans are set configurations meeting a specific problem of flow; the man of the art cannot extrapolate the results obtained from these designs. This study also made it possible to formulate the following conclusions:
From the pressure standpoint, the rotor behaves as a single stage thus offering the advantage of increasing the flow by increasing its length,
Only upstream/downstream asymmetry of stator shapes will determine the direction of flow,
For the same pressure/flow couple, it is possible to choose several combinations of diameter/length/speed of rotation combinations for the rotor.